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Krell KRC preamplifier Measurements

Sidebar 3: Measurements

The KRC's balanced output impedance at its line outputs measured just over 3 ohms (just over 2 ohms unbalanced). Its (line) input impedance measured just over 104k ohms (L) and just under 100k ohms (R), balanced, and just under 47k ohms unbalanced. The output impedance at the tape output was just under 45 ohms, regardless of the source impedance, indicating a buffered tape output.

The DC offset at the KRC's outputs measured under 0.3mV either channel, balanced or unbalanced. The preamp is noninverting from its inputs to its main outputs, and in the…

Krell Reference 64 digital processor

Remember the early days of CD, when some players were touted as having the revolutionary new "2x-oversampling" digital filters?

Those early oversampling players were the first to replace the analog output filter with one that operated in the digital domain, thereby avoiding the problems of steep analog filters. In fact, those analog filters were a significant source of unmusical sound in first-generation CD players, introducing severe phase shift, ringing, passband ripple, and often upper-treble attenuation. They were necessary, however, to remove the spurious images that appeared at…

Krell Reference 64 digital processor Page 2

Five digital inputs are provided: two on RCA jacks, one TosLink, one AES/EBU, and one ST-type optical. A digital in/out tape loop on RCA jacks (with an additional tape input on an ST-type jack) is included for driving a digital recorder. A sixth input on an ST-type jack, marked "Time Sync," allows the Reference 64 to lock to an external clock from Krell's transports. When the Time Sync connection is made between the Reference 64 and a Krell transport, the clock is sent separately instead of being recovered from the S/PDIF or AES/EBU datastream.

This technique can theoretically eliminate…

Krell Reference 64 digital processor Page 3

The PCM64 has a fairly high level of glitch in its output. DAC glitch is a spike of energy in the output signal when the converter changes state—as it does at every sample. To remove the PCM64's glitch, Krell designed a de-glitch circuit based on an AD841 op-amp. This is followed by another Analog Devices part, the AD846 op-amp used as a current-to-voltage (I/V) converter. The voltage output is then buffered by a PMI SSM2131 device. The de-emphasis circuit is built around the PMI output buffer. All this circuitry resides inside the aluminum DAC housing.

The Analog Domain
The analog…

Krell Reference 64 digital processor Page 4

This dynamic quality heard in the bass extended to the rest of the spectrum. The Reference 64 was particularly adept at portraying microdynamics—the small-scale transient aspect of music such as percussion, and the quickness of a drumstick hitting the drum head. The sound was the antithesis of slow, blurred, or fat. Macrodynamics—the sheer sense of slam and power—were also superb through the Reference 64. Orchestral climaxes were startling in their impact, a quality attributable to both the Reference 64's tremendous dynamics and lack of strain or congestion on peaks.

The Reference 64…

Krell Reference 64 digital processor Specifications

Sidebar 1: Specifications

Description: Digital/analog converter with 64x-oversampling digital filter. Inputs: two coaxial on RCA jacks, one AES/EBU on XLR jack, one TosLink optical, one AT&T ST-type optical, separate "Time Sync" clock input (two additional digital inputs are provided for tape monitoring, one coaxial, one ST-type optical). Conversion: custom Krell DAC modules. Digital filtering: DSP-based 64x-oversampling filter running custom Krell software. Frequency response: 4Hz–20kHz, –0.1dB. S/N ratio: 100dB (A-weighted). Linearity: ±0.3dB at –90dB. THD+N: 0.011%. Channel…

Krell Reference 64 digital processor Reference System

Sidebar 2: Reference System

I auditioned the Krell Reference 64 as part of my usual system, and also in the context of an all-Krell system comprising the KRC preamplifier, KSA-300S power amplifier, and DT-10 CD transport (with the Time Sync connection).

Most of the auditioning was through an Audio Research LS5 preamp driving the KSA-300S via the Reference 64's balanced outputs. CD transports driving the Reference 64 included Krell's top-of-the-line DT-10 (reviewed elsewhere in this issue) and the Mark Levinson No.31. Digital interconnects included a Madrigal AES/EBU cable, Aural…

Krell Reference 64 digital processor Measurements

Sidebar 3: Measurements

The Reference 64 had a maximum output level of 2.4V from the unbalanced outputs and 4.8V from the balanced jacks—exactly the 6dB increase expected. Channel balance—a measure of how closely matched the left- and right-channel output levels are to each other—was virtually perfect, with the right channel measuring just 0.03dB higher than the left. This excellent performance is no doubt due to the manual gain-trimming at the factory.

Output impedance was a low 16 ohms from the unbalanced outputs and 32 ohms from the balanced outputs, measured at any audio…

Magico Q5 loudspeaker

Show a time traveler from the 1920s an iPad and most likely he'd neither know what he was looking at nor what it might do. Show him a loudspeaker, even one as advanced as Magico's new Q5 ($59,950/pair), and he'd probably know exactly what it was and what it did, even if what it's made of might seem to have come from another planet.

It's been almost 100 years since two General Electric researchers, Rice and Kellogg (no cereal jokes, please), patented the basic design from which sprang all subsequent direct-radiating moving-coil drive-unit designs. While the general electrical,…

Magico Q5 loudspeaker Page 2

Marrying the drivers' surrounds to the smoothly radiused openings machined into the massive baffle and clamping them to the baffle's back give the Q5's face an unusually clean and elegant look. However, with no grille cover, should Junior, Fido, or the housekeeper (never you, of course) poke or slice a driver or its surround, replacing it would be a big job. But according to Wolf, the benefits of having no screws or bolts to inevitably loosen over time far outweigh the hassles of replacing drivers or surrounds, which Magico's dealers are trained to do.

The four-way, sealed-box design…